Inappropriate inspection practices at Nissan had been going for at least 20 years, Japan's national broadcaster NHK said today.
The new revelation could further roil Japan's second-biggest automaker.
Nissan said this week it was suspending domestic production of vehicles for the Japanese market for at least two weeks to address misconduct in its final inspection procedures, which it first revealed last month.
The scandal has led to a recall of all 1.2 million cars it sold in Japan over the past three years.
An internal investigation at Nissan had shown that for at least 20 years the car maker had not been following proper procedures for final inspections required by Japan's transport ministry of all vehicles sold in the country, NHK reported, without citing any sources.
Japan's Transport minister Keiichi Ishii said today that Nissan's inspection of its assembly plants was ongoing.
The Minister added that it remained unclear how long the final inspections had been conducted by uncertified technicians, a violation of ministry requirements.
A Nissan spokesman declined to directly confirm or deny the NHK report.
He referred to CEO Hiroto Saikawa's comments yesterday, when he said Nissan's training system for certifying vehicle inspection staff had not changed for 20 years.
Saikawa had added that was a separate issue from how long the misconduct had been going on.
He said that it appeared that a focus on increasing the efficiency of the inspection process and poor communication at assembly plants appeared to have contributed to the issue.
Nissan will continue to produce vehicles in Japan for export, including its popular Rogue SUV crossover model and the battery-electric Leaf, as the certification process for final inspections does not apply to vehicles shipped overseas.
The company produced roughly 79,300 passenger and commercial vehicles in Japan in August.
Around 27,600 of these were made for the domestic market, representing around 6% of its global production.
While Nissan has said the misconduct has no impact on the quality of its vehicles, it has raised questions about how closely rules are followed at its production plants, while also highlighting compliance issues at Japanese manufacturers.
Kobe Steel, Japan's third-biggest steelmaker, admitted this month it had falsified specifications on the strength and durability of aluminium, copper and steel products, misconduct that may have stretched back more than 10 years.